The present invention relates generally to electronic trip units. More specifically, the present invention relates to a method of determining contact wear of a circuit breaker at an electronic trip unit.
Electronic trip units (trip units) are well known. An electronic trip unit typically comprises voltage and current sensors which provide analog signals indicative of the power line signals. The analog signals are converted by an A/D (analog/digital) converter to digital signals which are processed by a microcontroller. The trip unit further includes RAM (random access memory), ROM (read only memory) and EEPROM (electronic erasable programmable read only memory) all of which interface with the microcontroller. The ROM includes trip unit application code, e.g., main functionality firmware, including initializing parameters, and boot code. The EEPROM includes operational parameters for the application code. An output of the electronic trip unit actuates a circuit breaker. The circuit breaker typically includes a pair of contacts which allows circuit current to pass from one contact member to another contact member. When the contacts open, circuit current is prevented from flowing from one contact member to the other and therefore, circuit current is prevented from flowing to a load which is connected to the breaker.
Circuit breaker contact wear, is a frequently occurring yet difficult to measure or predict problem because it is affected by a variety of factors. Contact wear is affected by the cumulative energy dissipated through arcing as breakers are opened. However, a single severe over-current fault can destroy contacts more quickly than several smaller faults, even though the smaller faults may add up to the same total energy dissipated. For example, some types of faults have more severe effects on contact wear than others, ground faults will destroy contacts more quickly than manual openings. Contacts are not generally easily inspected without costly disassembly and power down. However, if not detected contact wear may result in loss of power. The only current solution to this is defensive preventative maintenance whether required or not.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a method of detecting contact wear, at an electronic trip unit, of at least two pairs of separable contacts of a circuit breaker, the method comprising sensing temperature relative to a first pair of said at least two pairs of separable contacts to provide a first sensed contact temperature signal indicative thereof, sensing temperature relative to a second pair of said at least two pairs of separable contacts to provide a second sensed contact temperature signal indicative thereof, comparing said first and second sensed contact temperature signals to provide a differential contact temperature signal, and analyzing said differential contact temperature signal to assess contact wear of said pairs of separable contacts.
The above discussed and other drawbacks and deficiencies are also overcome or alleviated by a breaker assembly comprising an electronic trip unit and a circuit breaker having at least two pairs of separable contacts, said breaker assembly further comprising a sensor positioned for sensing temperature relative to a first pair of said at least two pairs of separable contacts to provide a first sensed contact temperature signal indicative thereof, a sensor positioned for sensing temperature relative to a second pair of said at least two pairs of separable contacts to provide a second sensed contact temperature signal indicative thereof, and a signal processor responsive to said first sensed contact temperature signal and said second sensed contact temperature signal, and having memory for storing signals including program signals defining an executable program which compares said first and second sensed contact temperature signals to provide a differential contact temperature signal, and analyzes said differential contact temperature signal to assess contact wear of said at least two pairs of separable contacts.
The above discussed and other features and additional advantages of the present invention will be appreciated and understood by those skilled in the art from the detailed description and drawing.